More How eBikes Work from EVELO

Electric Bikes: How Watts, Volts, and Amp Hours Impact Performance

Adapted from: https://evelo.com/blogs/learn/electric-bikes-how-watts-volts-and-amp-hours-impact-performance

If you want to compare ebike power ratings, you need to understand watts (W), volts (V), and amp-hours (Ah). ‘Rated power,’ the metric some manufacturers use, doesn’t equal a motor’s actual power output or maximum potential power output.

An electric bike owner or shopper needs to understand how these electrical measurements impact an ebike’s performance.

Electric Bikes: Watts

In most cases, the watt rating on an electric bike motor describes how much energy the motor can handle (or consume) continuously. It is different from a peak watt rating that describes how much energy the motor can manage for short periods of time. Some eBike may have a continuous rating of 250 watts while having a peak rating of 500 watts. That can make a huge difference when climbing a hill. Be sure to get BOTH ratings.

CONFIGURATION IMPACTS POWER

Depending on the ebike’s configuration, the amount of power at the wheel can differ greatly for motors with identical watt ratings. A wattage rating may be the least indicative measurement. An ebike’s controller, battery, and location of the drive can have a lot more to do with how an ebike performs.

When electric bikes first began gaining popularity, motors located in the wheel hub were the most frequently used type of motor. Subsequently, mid-drive motors located at the crank set appeared where they can work in tight coordination with the bike’s already existing gears, amplifying their mechanical advantage. 

This becomes particularly helpful for climbing steep hills or navigating extended inclines.

Thus in some cases, an ebike with a mid-drive motor rated for, perhaps, 350W of continuous energy may have more “power” than a hub-drive ebike with 500W or even 750W..

Electric Bikes: Volts

Volts describe the potential power (electromotive force) in an ebike system. Ebike batteries usually have volts in sequences of 12 such as 12, 24, 36, 48, etc. Volts pretty much mean power — how powerful a battery can be, and it implies top speed.

When climbing steep hills, a 48V battery will outperform a 36V because the latter must work harder to produce the same results. It can be very important to look at the number of volts in an electric bike battery relative to the bicycle’s entire configuration.

Electric Bikes: Amp Hours

Amp-hours are an indication of the capacity of the ebike’s battery or potential range for the bike. A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before becoming completely discharged. 

Because real batteries don’t behave in a simple linear discharge fashion, amp-hour capacity is specified at either a given current, given time, or assumed to be rated for a time period of 8 hours.

Nevertheless, higher amp hours generally means higher range. But it is not an exact mathematical formula for volts, speed, amp-hours, and distance since bikes and riders are not that precise. Some riders pedal more often thereby adding energy and extending range and speed.

Electric Bike: Watt, Volt, and Amp Hour Resources

• “The Complete Electric Bike Buyer’s Guide,” is a comprehensive guide for understanding how to compare electric bikes.
• “E-Bike Motors, Explained,” is Dan Roe’s Bicycling magazine article. Well worth a read.
• “Ebike Volts VS Amp Hours,” is the Blue Monkey Bikes video featuring Michael Geurts which was quoted extensively in this article.
• “What Are The Differences Between Motor Types on Electric Bikes” explains the difference between the types of motors that may be used on your electric bike.
• “Which is better: 48V or 52V battery?” in this video electric bike expert, Micah Toll, explains the difference between lead-acid and lithium battery cells and how that difference impacts the batteries used for bikes.
• “How Much Power Does An Electric Bicycle Need?” also by Micah Toll.
• “Batteries And Power Systems” is chapter 11 of Tony R. Kuphaldt’s book, “Lessons in Electric Circuits.”
• “Electric Circuits, Hydraulic Analogy: Charge, Voltage, and Current (introduction)” is the Gary Chang video referenced in this article. Chang has many excellent and applicable videos on his YouTube channel.
• “How Much Battery Range Do I Need?” compares amp hours to electric bike range.
• “How do I maximize the battery life of my electric bike?” describes how to maintain and treat your ebike battery.
• “How do I increase the range of my electric bike’s battery?” explains what you can do to get more range on a single charge.
• “How Electric Bike Throttles and Pedal Assist Work” this video explains pedal assistance and throttles.